Public Release: 10-Jun-2009
Predicted ground motions for great earthquake in Pacific Northwest: Seattle, Victoria and Vancouver

June 8, 2009 -- A new study evaluates expected ground motion in Seattle, Victoria and Vancouver from earthquakes of magnitude 7.5 - 9.0, providing engineers and policymakers with a new tool to build or retrofit structures to withstand seismic waves from large "subduction" earthquakes off the continent's west coast.

The Cascadia subduction zone in the Pacific Northwest has produced great earthquakes of magnitude 9.0 and larger, most recently in the 1700s. Now home to millions of people and a vast infrastructure of buildings and other man-made structures, scientists seek to determine the impact of large earthquakes on the region.

To simulate ground motions from a very large earthquake on the local region, this study combined detailed analysis of ground motions recorded from smaller earthquakes in the Pacific Northwest with recorded data from a severe subduction earthquake from another region - the M8.4 2003 Tokachi-Oki quake off the coast of Japan. The authors estimate ground motions for firm ground at the three sites and provide a model that engineers can adjust for local or site-specific soil conditions.

Co-author Gail Atkinson of the University of Western Ontario describes earthquakes in the Pacific Northwest as having rich energy content. "The expected ground motion may not be very large in amplitude - the peak accelerations are not that high - but the motion will go on for a very long time," Atkinson explained. "The real hazard is that an earthquake here will affect a very large, very wide region - amplifying seismic motion and exciting vulnerable structures wherever there is an opportunity to do so."

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Article: Bulletin of the Seismological Society of America, volume 99:3; "Predicted Ground Motions for Great Interface Earthquakes in the Cascadia Subduction Zone" by Gail M. Atkinson and Miguel Macias.

About BSSA: The Bulletin of the Seismological Society of America (ISSN 0037-1106) is the premier journal of advanced research in earthquake seismology and related disciplines. It first appeared in 1911 and was issued on a quarterly basis until 1963. Since 1963, it has appeared bimonthly (in February, April, June, August, October, and December). Each issue is composed of scientific papers on the various aspects of seismology, including investigation of specific earthquakes, theoretical and observational studies of seismic waves, inverse methods for determining the structure of the Earth or the dynamics of the earthquake source, seismometry, earthquake hazard and risk estimation, seismotectonics, and earthquake engineering.

About SSA: The Seismological Society of America is a scientific society devoted to the advancement of earthquake science. Founded in 1906 in San Francisco, the Society now has members throughout the world representing a variety of technical interests: seismologists and other geophysicists, geologists, engineers, insurers, and policy-makers in preparedness and safety.

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